An ang adsorbent and a method for preparing the same

Abstract

The application belongs to the field of adsorbents, and particularly relates to an ANG (adsorbed natural gas) adsorbent and a preparation method thereof. In order to solve the problem that the existing modification method of adsorbents is difficult to synergistically optimize multiple performances, the preparation method of the ANG adsorbent comprises the following steps: raw material selection and pretreatment, carbonization and activation, washing and drying, crushing and screening, post-treatment and modification, and the like. The post-treatment and modification are selected from at least one of metal ion loading modification, mild heat treatment modification and surface chemical modification. The metal ion loading modification can enhance the affinity for methane, the mild heat treatment modification can control the pore size, and the surface chemical modification can improve the hydrophobicity. Through the above combinable modification schemes, the high-performance adsorbent with high methane adsorption capacity, optimized pore size structure and strong hydrophobicity can be prepared.

Description

Technical Field

[0001] This invention belongs to the field of adsorbents, specifically relating to an ANG (adsorbent natural gas) adsorbent and its preparation method. Background Technology

[0002] Adsorption-based natural gas technology is an advanced gas storage method that increases gas storage density by filling storage tanks with porous adsorbents (such as activated carbon) with high specific surface area. The microporous structure of the material allows for the physical adsorption of natural gas molecules under relatively low pressure.

[0003] To further improve adsorbent performance, existing technologies typically modify basic materials such as activated carbon. For example, loading specific metals or metal oxides onto the surface of activated carbon can enhance its adsorption affinity for methane molecules. However, while these methods can increase the adsorption capacity of the target gas, they often overlook interference from other components present in actual operating conditions. In particular, water vapor, which is prevalent in natural gas, competes with methane molecules for adsorption on the adsorbent surface, significantly reducing the effective gas storage performance of the adsorbent. Furthermore, conventional methods that adjust pore structure through heat treatment are difficult to achieve precise control of pore size distribution without significantly sacrificing the material's specific surface area.

[0004] Therefore, existing modification methods are usually single-minded, only optimizing one performance index of the adsorbent. There is a lack of a preparation method that can systematically and synergistically optimize multiple key properties of the adsorbent (such as methane affinity, pore structure, and hydrophobicity), resulting in the overall performance of the prepared adsorbents failing to meet the increasingly stringent practical application requirements.

[0005] Therefore, based on this, the technical solution of the present invention is proposed. Summary of the Invention

[0006] The purpose of this application is to overcome the aforementioned deficiencies of the prior art and provide an ANG adsorbent and its preparation method. This method can optimize the methane adsorption capacity, pore structure, and hydrophobic and moisture-resistant properties of the adsorbent individually or in combination according to different performance optimization requirements, thereby obtaining an adsorbent product with excellent overall performance.

[0007] To address the problems existing in the prior art, the present invention provides a method for preparing ANG adsorbent, the method comprising the following steps:

[0008] (1) The wood raw materials are crushed, screened and impurities are removed to obtain pretreated raw materials;

[0009] (2) The pretreated raw materials are sequentially carbonized, pyrolyzed and activated to generate a porous structure and obtain activated carbon;

[0010] (3) The activated carbon is cleaned and dried to prevent pore blockage, and dried activated carbon is obtained;

[0011] (4) The dried activated carbon is pulverized and sieved to obtain pulverized activated carbon;

[0012] (5) The pulverized activated carbon is post-treated and modified to adjust the surface chemical properties and pore size distribution (adsorption pore size is 3.3~4nm) of the pulverized activated carbon, thereby enhancing its adsorption capacity for ANG and finally obtaining the ANG adsorbent.

[0013] Preferably, in step (1), the woody raw material is coconut shell. When selecting raw materials, materials with high carbon content and few impurities should be chosen, such as coconut shell, woody raw materials, coal-based raw materials, etc.

[0014] Preferably, in step (2), the carbonization pyrolysis is performed by pyrolyzing the pretreated raw material under oxygen-deficient conditions at 400~900℃. The equipment used in this process is a carbonization furnace, such as a rotary kiln carbonization furnace or a vertical carbonization furnace.

[0015] Preferably, in step (2), the activation method is: the raw material after carbonization and pyrolysis is treated by physical activation, chemical activation, or a combination of physical and chemical activation; wherein:

[0016] The physical activation method is as follows: the raw material after carbonization and pyrolysis is brought into contact with an activation gas at 800~1000℃, and the pores are expanded by gas etching to form a microporous structure; the activation gas is water vapor or carbon dioxide; the equipment used in this process is an activation furnace (such as a Sleip activation furnace), a gas supply system, etc.

[0017] The chemical activation method is as follows: the raw material after carbonization and pyrolysis is mixed with a chemical activator to promote the formation of pores in the raw material; the chemical activator is phosphoric acid, zinc chloride or potassium hydroxide; the equipment used in this process is mixing equipment, activation reactor, etc.

[0018] The physical-chemical combined activation method involves sequentially employing chemical activation and physical activation to optimize the pore structure and specific surface area of ​​the raw materials.

[0019] Preferably, in step (3), the activated carbon is cleaned and dried by acid washing or water washing to prevent pore blockage and obtain dried activated carbon. The equipment used in this process is washing equipment (such as washing tank, filter) and drying equipment (such as dryer, vacuum drying oven).

[0020] Preferably, in step (4), the dried activated carbon is pulverized into small particles as needed and sieved to obtain products within the required particle size range. The equipment used is a pulverizer (such as a ball mill or hammer crusher) or a screening device (such as a vibrating screen).

[0021] Preferably, in step (5), the post-treatment and modification method is: mild heat treatment modification, metal ion loading modification, or surface reduction-carbon deposition modification. The equipment used in this process is modification equipment (such as heat treatment furnace or chemical impregnation equipment).

[0022] It should be noted that when the purposes of "post-processing and modification" are different, the methods will also be different, specifically:

[0023] (i) When the goal is to “precisely control the pore size of the adsorbent”, a “mild heat treatment” modification method should be adopted. The purpose is to eliminate the unstable pore structure of the adsorbent in order to achieve an adsorption pore size of 3.3~4nm.

[0024] (ii) When the objective is to "enhance the methane affinity of the adsorbent", a "metal ion loading" modification method should be used, the function of which is to introduce Cu. 2+ / Ni 2+ The CH4 adsorption energy of the adsorbent is enhanced through weak chemical bonds (π complexation).

[0025] (iii) When the purpose is to “improve the hydrophobicity of the adsorbent”, the “surface reduction-carbon deposition” modification method should be adopted. The function is to reduce the oxygen-containing groups on the surface of the adsorbent and avoid competitive adsorption of water vapor.

[0026] (iv) When the objective is to "optimize the bulk density of the adsorbent," a modification method of "particle shaping and classification" should be adopted to improve the tank filling rate. Here, the tank refers to a container with ANG adsorbent adsorbent attached to its inner wall, also known as an "ANG tank," used for storing natural gas. Specifically, by filling the tank (or bottle) with high specific surface area nano-ANG adsorbent (such as activated carbon particles), the specific surface area can reach 1800 m² after aeration due to its microporous structure. 2 / g and adsorbs methane from natural gas. At room temperature and low pressure (4 MPa), methane molecules are adsorbed on the microporous surface, and the gas is released by desorption through pressure difference during use.

[0027] Preferably, the mild heat treatment modification method includes the following steps:

[0028] (S1) Under an inert atmosphere, the pulverized activated carbon is heated from room temperature to 300-500℃ at a rate of 3-4℃ / min; wherein:

[0029] The inert atmosphere is nitrogen or argon;

[0030] (S2) Keep warm for 0.5~2h to reduce the micropore size of the pulverized activated carbon to 3.3~4nm.

[0031] Preferably, the metal ion-supported modification method includes the following steps:

[0032] (SS1) Dissolve the modifier in water and add ethanol to obtain the impregnation solution; wherein:

[0033] The modifier is one or a combination of two or more of CuCl2, Cu(NO3)2, and NiCl2; CuCl2 has a high cost-performance ratio and significant effect, Cu(NO3)2 has uniform loading but requires prevention of residue, and NiCl2 has stronger adsorption but higher cost.

[0034] The concentration of the modifier is 0.1~0.5 mol / L;

[0035] (SS2) The pulverized activated carbon is introduced into the impregnation solution and stirred for adsorption; wherein:

[0036] The stirring time is 2-4 hours, and the liquid-to-solid ratio is 1.5-2.5:1 (mL:g).

[0037] (SS3) After filtration, discard the impregnation solution, retain the precipitate and dry it at 60~70℃ for 2~3 hours;

[0038] (SS4) Under an inert atmosphere, the precipitate is heated to 250-350°C at a rate of 5-6°C / min and held at that temperature for 1-2 hours.

[0039] When the modifier is CuCl2, it decomposes CuCl2 into highly dispersed CuO / Cu2O active sites. Caution: Temperatures above 400℃ will cause Cu particles to sinter and agglomerate.

[0040] Preferably, the surface reduction-carbon deposition modification method includes the following steps:

[0041] (SSS1) Place the pulverized activated carbon in an inert atmosphere;

[0042] (SSS2) Heat to 400-600℃ at 10-12℃ / min and hold for 1-1.5h to remove oxygen-containing groups (carboxyl groups, phenolic hydroxyl groups) on the surface of the pulverized activated carbon.

[0043] (SSS3) Maintain an inert atmosphere and allow to cool naturally to room temperature.

[0044] The beneficial effects of this invention are as follows:

[0045] The ANG adsorbent and its preparation method provided by this invention, through optimized raw material selection, carbonization and activation process and targeted post-treatment and modification steps, can prepare adsorbents with small particles, precise adsorption pore size control of 3.3~4nm and excellent performance, significantly improving the adsorption capacity for specific substances (especially methane), while improving key indicators such as hydrophobicity and bulk density, meeting the practical needs of ANG systems, and featuring strong process controllability, stable performance and high application value.

[0046] 1. Precisely control the pore structure to improve adsorption efficiency. Through steps such as raw material pretreatment, activation condition control and mild heat treatment, the average pore size of the adsorbent can be precisely controlled to the optimal range of 3.3~4nm, while retaining the well-developed microporous structure and high specific surface area, providing sufficient adsorption sites for substances such as methane, and significantly improving the adsorption capacity (e.g., the methane adsorption capacity increased by 24% in the case).

[0047] 2. Enhance the affinity for target substances and optimize adsorption performance by using metal ion loading (such as CuCl2) modification, through the introduction of Cu 2+ / Ni 2+ By utilizing active sites and π-complexation to enhance the adsorption energy of methane, this method solves the problem of insufficient adsorption capacity of traditional adsorbents for specific substances. Furthermore, the method is cost-effective, has uniform loading, and is suitable for large-scale applications.

[0048] 3. Improve hydrophobicity and reduce environmental interference. After surface reduction-carbon deposition modification, the oxygen-containing groups on the adsorbent surface are reduced, and the water vapor adsorption rate is significantly reduced (such as a 33% decrease in the case). This effectively avoids the competitive adsorption of water vapor on the target substance and ensures that the adsorption performance remains stable in humid environments.

[0049] 4. Optimize bulk density and improve practical value. Through modification methods such as particle shaping and grading, the bulk density of the adsorbent is improved (e.g., 51.1% increase in the case study), which can increase the filling rate of the ANG storage tank, increase the energy storage density per unit volume, and better meet the needs of storage tank space utilization in practical applications.

[0050] 5. The process is highly controllable and facilitates industrial production. The parameters such as temperature, time, and reagent dosage of the entire preparation process (including carbonization, activation, and modification steps) are clearly controllable. The equipment for each step (such as rotary kiln carbonization furnace and Sleip activation furnace) is mature, and the modification methods (such as metal loading and mild heat treatment) are easy to operate. It can stably produce high-performance adsorbents and is suitable for large-scale industrial promotion. Detailed Implementation

[0051] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0052] Example 1

[0053] This embodiment provides a method for preparing an ANG adsorbent, the method comprising the following steps:

[0054] (1) Select coconut shells rich in carbon and with natural porous structure as raw materials, mechanically crush them, and sieve them through a standard sieve to obtain particles with a particle size in the range of 250~450μm to ensure the uniformity of subsequent processing. After removing impurities, pre-treated raw materials are obtained.

[0055] (2) The pretreated raw material (impurity-removed coconut shell particles) is placed in a carbonization furnace under an inert atmosphere (such as nitrogen) and carbonized at 800°C for 2 hours. This is to remove volatile substances from the raw material and form a preliminary carbon skeleton structure. After carbonization, the resulting carbon is transferred to an activation furnace, where steam is introduced as an activator and activated at 900°C for 3 hours. The steam reacts with the carbon atoms, thereby etching out a rich microporous structure, significantly increasing the specific surface area of ​​the material, and obtaining activated carbon.

[0056] (3) After activation, the activated carbon is acid washed, usually by soaking in dilute hydrochloric acid to remove inorganic ash impurities and prevent pore blockage. Then it is washed repeatedly with deionized water until the pH of the filtrate is close to neutral (e.g., pH=7). The washed activated carbon is dried in an oven at 110°C for 12 hours to completely remove moisture and obtain dry activated carbon.

[0057] (4) The dried activated carbon is pulverized and sieved again to obtain pulverized activated carbon with uniform particle size (average pore size of about 3.1 nanometers). The pulverized activated carbon prepared in this step has a high specific surface area and a preliminary pore network, which provides an excellent base for subsequent modification treatment.

[0058] (5) Post-treatment and synergistic modification of pulverized activated carbon, specifically:

[0059] (5-1) Accurately weigh a certain amount of copper chloride dihydrate (CuCl2·2H2O), dissolve it in deionized water, and prepare a copper chloride aqueous solution with a concentration of 0.3 mol / L. This is the impregnation solution. It is understood that, in order to enhance the wetting ability of the impregnation solution on the highly hydrophobic activated carbon surface and ensure that copper ions can more effectively penetrate into the internal pores of the activated carbon, 5% anhydrous ethanol is added to the prepared copper chloride solution, and the mixture is stirred thoroughly. Ethanol, as a surfactant, can reduce the surface tension of the solution and promote the spreading of the liquid phase on the solid surface.

[0060] (5-2) Place 100g of precisely weighed pulverized activated carbon into an impregnation apparatus (e.g., a beaker with a magnetic stirrer). Then, measure 180mL of the prepared impregnation solution and slowly add it to the impregnation apparatus containing the pulverized activated carbon. The liquid-to-solid volume ratio here is approximately 1.8:1, which ensures that all activated carbon particles are adequately covered by the impregnation solution. Turn on the magnetic stirrer and stir continuously for 3 hours at room temperature (approximately 25°C). Continuous stirring helps to break up the liquid film around the particles, promoting the mass transfer of copper ions from the bulk liquid phase to the inner and outer surfaces of the activated carbon, thereby ensuring uniform adsorption and distribution of copper ions on the activated carbon matrix.

[0061] (5-3) After impregnation, solid-liquid separation and pre-drying are performed. The mixture in the impregnation device is separated by a filtration device (e.g., a Buchner funnel with a vacuum filtration system) to obtain impregnated activated carbon particles. To remove as much free solution as possible from between the particles, the filter cake can be appropriately compacted. The separated wet activated carbon is then transferred to a pre-drying device (e.g., a constant temperature forced-air oven) and pre-dried at 60°C for 2 hours. This step aims to remove physically adsorbed moisture and ethanol from the surface and macropores of the activated carbon to avoid particle breakage or changes in the distribution of the loading due to rapid evaporation of moisture during subsequent high-temperature heat treatment. At the same time, this lower temperature will not cause premature decomposition of copper chloride.

[0062] (5-4) Finally, the crucial thermal decomposition synergistic modification step was performed. The pre-dried copper-loaded activated carbon sample was uniformly spread in a quartz boat and placed in the isothermal zone of a tube furnace. High-purity nitrogen gas was introduced into the furnace tube at a flow rate of 100 mL / min through the sealed nitrogen inlet for 30 minutes to completely purge any residual air and create an inert protective atmosphere for the thermal decomposition reaction. Subsequently, the temperature control program of the tube furnace was started, and the furnace temperature was increased from room temperature to 300℃ at a linear heating rate of 5℃ / min, and maintained at this temperature for 2 hours. During this process, copper chloride adsorbed in the pores of the activated carbon underwent thermal decomposition, forming highly dispersed copper oxide or elemental copper active sites. These newly generated sites can interact more strongly with methane molecules through π-complexation and other forces, thereby significantly enhancing the affinity of the adsorbent for methane. Meanwhile, the 300℃ heat treatment falls within the mild heat treatment range (300~500℃). This temperature provides sufficient energy for the carbon atoms at the edges of the activated carbon micropores to undergo microscopic rearrangement, resulting in a slight and controllable expansion of some pore openings. This increases the overall average pore size (measured to 3.4 nm, see Table 1 below), thus bringing it closer to the optimal adsorption pore size for methane molecules. Furthermore, the entire heat treatment process is conducted in an oxygen-deficient environment under nitrogen protection. The high temperature helps some unstable oxygen-containing functional groups (such as carboxyl groups) on the activated carbon surface decompose and detach, converting them into gases such as carbon dioxide or carbon monoxide, which are then discharged from the exhaust outlet with the tail gas. This reduces surface polarity and improves the hydrophobicity of the adsorbent. After the heat treatment is completed, heating is stopped, and the tubular furnace is allowed to cool naturally to room temperature under continuous nitrogen protection. The sample removed after cooling is the final product, ANG (adsorbed natural gas) adsorbent.

[0063] In addition, as an optional optimization, the final adsorbent particles prepared in this embodiment can be further modified by particle shaping and grading. For example, irregular particles can be shaped to be more spherical using specific granulation or spheroidizing equipment, and then precisely graded using a series of sieves with different pore sizes to obtain a finished product with a narrower particle size distribution. This treatment can significantly improve the packing density and filling uniformity of the adsorbent in the storage tank, thereby further increasing the total gas storage capacity per unit tank volume on a macroscopic scale.

[0064] Example 2

[0065] This embodiment provides a variation of the preparation method for a high-performance adsorption-type natural gas adsorbent, aiming to verify the universality of metal ion loading modification and explore the influence of different metal species on performance. In this embodiment, nickel ions are used instead of copper ions in Example 1 as the modifying species. Nickel may have a stronger interaction with methane molecules, potentially leading to higher methane adsorption performance.

[0066] This embodiment provides a method for preparing an ANG adsorbent, which is summarized as follows:

[0067] First, steps (1) to (4) are exactly the same as in Example 1, and the average pore size of the pulverized activated carbon obtained is about 3.1 nanometers.

[0068] Secondly, the "post-processing and co-modification" in step (5) is different from that in Example 1, as follows:

[0069] (5-1) Dissolve nickel chloride hexahydrate (NiCl2·6H2O) in deionized water to prepare a nickel chloride impregnation solution with a concentration of 0.2 mol / L. Similarly, to improve wettability, add a small amount of ethanol to the solution.

[0070] (5-2) Immerse 100g of pulverized activated carbon in an appropriate amount of nickel chloride impregnation solution and stir for several hours at room temperature. Then, perform solid-liquid separation through a filtration device, and pre-dry the resulting wet filter cake at 60°C in a pre-drying device.

[0071] (5-3) The pre-dried nickel-loaded activated carbon was placed in a tube furnace and heat-treated under the protection of high-purity nitrogen introduced through the nitrogen inlet. Considering that the thermal decomposition temperature of nickel chloride is slightly higher than that of copper chloride, in order to ensure that it can fully decompose to form highly active metal or metal oxide sites, the thermal decomposition activation temperature was set at 380℃ in this embodiment. The heating program also adopted a rate of 5℃ / min, and after reaching 380℃, it was held at this temperature for 1.5h. The temperature of 380℃ can not only effectively promote the decomposition of nickel chloride, but also falls within the mild heat treatment range (300~500℃) and close to the surface chemical modification range (400~600℃), so it can also play a synergistic role in regulating pore size and improving hydrophobicity. After the holding period, it was naturally cooled to room temperature in a nitrogen atmosphere to obtain the final product ANG adsorbent (nickel-modified high-performance adsorbent).

[0072] Example 3

[0073] This embodiment provides another variation of the method for preparing high-performance adsorption-type natural gas adsorbents. Its main objective is to maximize the hydrophobic properties of the adsorbent, making it particularly suitable for applications where the water vapor content in the natural gas feedstock is extremely high. The core of this embodiment lies in using a higher heat treatment temperature than in Embodiments 1 and 2 to deeply treat the basic activated carbon under an inert atmosphere, thereby more thoroughly removing the hydrophilic functional groups on the surface.

[0074] This embodiment provides a method for preparing an ANG adsorbent, which is summarized as follows:

[0075] First, steps (1) to (4) are exactly the same as in Examples 1 and 2, and the average pore size of the pulverized activated carbon obtained is about 3.1 nanometers.

[0076] Secondly, the "post-processing and co-modification" in step (5) is different from that in Examples 1 and 2, as follows:

[0077] (5-1) Spread 100g of pulverized activated carbon evenly inside a quartz boat. Then, push the quartz boat containing the sample into the central isothermal zone of the tube furnace. After sealing the tube furnace, introduce high-purity nitrogen into the furnace through the nitrogen inlet at a flow rate of 200mL / min and continue to ventilate for 30min to ensure that the air inside the furnace is completely replaced.

[0078] (5-2) Start the temperature control system connected to the tube furnace, set the program to heat the furnace temperature from room temperature to 600°C at a heating rate of 10°C per minute, and maintain this temperature for 1 hour. At such a high temperature of 600°C and in a completely oxygen-deficient environment, the main oxygen-containing hydrophilic groups on the surface of activated carbon, such as carboxyl groups (-COOH) and phenolic hydroxyl groups (-OH), will undergo thermal decomposition or carbothermic reduction reactions. For example, carboxyl groups decompose into carbon dioxide and water and are removed, and phenolic hydroxyl groups may also be reduced. These reactions effectively remove the polar sites that give the carbon material its hydrophilicity, exposing more of the graphitized microcrystalline structure of carbon. These exposed carbon six-membered ring structures are themselves nonpolar and strongly hydrophobic. Throughout the process, the gaseous products generated by the reaction will be discharged from the tail gas outlet along with the nitrogen gas flow.

[0079] (5-3) After the heat preservation is completed, turn off the heating power, but continue to keep the nitrogen gas flowing until the tube furnace cools down to room temperature naturally. Take out the sample to obtain the final product ANG adsorbent (a high-performance adsorbent that has undergone deep hydrophobic modification).

[0080] Example 4

[0081] This embodiment provides another variation of the method for preparing high-performance adsorbents for natural gas. Its main objective is to precisely control the pore size of a basic activated carbon with an initially large pore size, making its pore size distribution better suited to the needs of adsorbent natural gas applications. The core of this method lies in using precisely controlled, mild heat treatment conditions to achieve fine-tuning and shrinkage of the pore size without significantly reducing the specific surface area.

[0082] This embodiment provides a method for preparing an ANG adsorbent, which is summarized as follows:

[0083] First, in this embodiment, a pulverized activated carbon was prepared using a chemical activation method (e.g., phosphoric acid method) different from that of Example 1. The pulverized activated carbon is characterized by a very high specific surface area, but its average pore size is relatively large, measured to be approximately 4.5 nm. While a high specific surface area is beneficial for providing more adsorption sites, an excessively large pore size leads to a decrease in the filling efficiency of gas molecules at a given pressure, which is detrimental to achieving a high volumetric storage density.

[0084] Secondly, the "post-processing and synergistic modification" in step (5) is different from that in Examples 1 to 3, as follows:

[0085] (5-1) Precise pore size control modification was performed on the above-mentioned large-pore pulverized activated carbon. This pulverized activated carbon with an average pore size of 4.5 nm was placed in a tube furnace. To ensure the purest processing environment, high-purity argon was selected as the protective gas in this embodiment and introduced through the gas inlet.

[0086] (5-2) Start the temperature control system and set a slow heating rate, such as 3℃ / min, to ensure uniform heating of the entire sample bed and avoid local overheating. Slowly heat the furnace to 480℃. In this embodiment, the heat treatment temperature is preferably 480℃, which is within the mild heat treatment range of 300~500℃. This temperature provides sufficient energy to induce the migration and recombination of carbon atoms at the edges of the microcrystalline graphite sheets, but is insufficient to cause large-scale ablation of the carbon skeleton or collapse of the pore walls.

[0087] (5-3) The temperature is precisely kept at 480℃ for 1 hour. During this period, the unstable carbon atoms with higher energy in the pore openings or channels of the activated carbon micropores relax and rearrange, tending to form a more stable structure. This process is macroscopically manifested as a slight contraction of the pore openings of some micropores, thereby reducing the overall average pore size.

[0088] (5-4) After the heat preservation is completed, the tube furnace is allowed to cool naturally to room temperature under the continuous protection of the argon atmosphere. The sample is then removed, and the final product ANG adsorbent (an adsorbent with precisely controlled pore size) is obtained.

[0089] The pore size-controlled adsorbent prepared by this invention exhibits significant adaptability in various practical scenarios such as natural gas storage, recovery, and energy supply. Specific applications are as follows:

[0090] 1. LNG (Liquefied Natural Gas) BOG (Bottle-Off Gas) Recovery Scenarios

[0091] During LNG storage and transportation, BOG (bound gas) generated by natural LNG evaporation (temperature pretreated to ambient temperature, pressure 0.1-0.5 MPa, water content <1 ppm) needs to be efficiently recovered using adsorbents. The adsorbent of this invention can be filled into a fixed-bed adsorption tower, utilizing its high specific surface area and precise pore structure to efficiently capture BOG gas at ambient temperature and low pressure. Once adsorption is saturated, natural gas is released through depressurization desorption, which can be directly reinjected into LNG storage tanks or used as fuel gas. Simultaneously, this adsorbent exhibits good temperature resistance, tolerating temperature fluctuations during the adsorption-desorption process, and can be regenerated periodically by hot nitrogen purging, preventing impurity deposition that reduces adsorption capacity. The BOG recovery rate can reach over 95%, making it suitable for urban LNG storage and transportation, LNG ocean shipping, and ship power supply scenarios.

[0092] 2. Wellhead gas and scattered gas recovery scenarios

[0093] Addressing the characteristics of low pressure and large flow fluctuations in wellhead gas (such as shale gas and coalbed methane) and scattered gas, the adsorbent of this invention is suitable for low-pressure adsorption requirements: Pre-treated gas sources are pressurized to 3-5 MPa by a compressor and then introduced into a mobile ANG storage tank assembly filled with the adsorbent, where the gas is efficiently adsorbed and stored. When gas is needed, it can be depressurized and desorbed for direct use in well site power generation or heating, or transported to a gas gathering station for connection to the main pipeline network. This adsorbent reduces the energy consumption of traditional high-pressure gas storage and is suitable for remote well sites without pipeline networks, avoiding the waste of scattered natural gas venting and improving resource utilization.

[0094] 3. Urban natural gas peak shaving scenario

[0095] In urban natural gas transmission and peak shaving, the adsorbent of this invention can be filled into ANG storage tanks. Utilizing its low-pressure adsorption characteristics, it connects to the high-pressure pipeline network to adsorb natural gas during off-peak gas demand and connects to the low-pressure pipeline network to desorb and supply gas during peak demand. Its modular design enables a storage tank volume utilization rate of 92%, shortening the peak shaving response time to 2 hours, allowing for rapid response to urban gas demand fluctuations. Simultaneously, the microporous structure of the adsorbent can filter impurities such as hydrogen sulfide and water vapor from natural gas, reducing pipeline corrosion and maintenance costs. Furthermore, the small size and minimal footprint of the storage tank make it suitable for core areas of cities with limited land resources.

[0096] 4. Industrial scenarios for gas welding, gas cutting, and thermal spraying

[0097] In industrial gas welding, gas cutting, and thermal spraying operations, adsorbents can store natural gas in ANG gas cylinders, utilizing their low-pressure slow-release characteristics to ensure a stable release of natural gas: during gas welding, combustion is clean and produces no harmful gases or carbide slag, optimizing the working environment; during gas cutting, preheating time is short, cutting speed is fast, kerf is small and slag removal is unnecessary, and the cut surface is free of carbon buildup and hardening; during thermal spraying, a stable heat source is provided, avoiding contamination of the coating material. Furthermore, the pore size regulation characteristics of the adsorbent ensure that the gas adsorption-desorption rate matches the operational requirements, and low-pressure storage reduces the risk of cylinder explosions, making it suitable for harsh industrial operating environments. At the same time, the cost of the gas is 40%-80% lower than that of traditional acetylene and propane.

[0098] 5. Distributed energy scenarios in remote / pipeline-free areas

[0099] In remote areas without natural gas pipelines (such as civilian use in Africa and mountainous areas in China), the adsorbent of this invention enables miniaturized storage of natural gas: after filling ANG gas cylinders with the adsorbent, natural gas can be stored at a low pressure of 4MPa, which is convenient for transportation and has no risk of accumulation and explosion after leakage, making it suitable for the distribution needs of areas with complex terrain; when used for domestic cooking, it produces no black smoke or pollutants, reducing indoor PM2.5 pollution and carbon emissions; at the same time, it can be used as fuel for well site generators and for temporary mobile gas stations, without the need for complex pressurization equipment, and can be filled directly through pressure difference convection to meet the clean energy supply needs of remote areas.

[0100] 6. On-board fuel alternative scenarios

[0101] In vehicle-mounted gas systems, the adsorbent of this invention can replace the traditional high-pressure storage mode of CNG (compressed natural gas): its low-pressure adsorption characteristics make the pressure of the vehicle-mounted storage tank only 1 / 5 to 1 / 4 of that of CNG, reducing the weight of the storage tank and material costs, and improving driving safety; at the same time, the precisely controlled pore size and high specific surface area ensure that the gas storage capacity meets the vehicle's range, and can be used as an energy solution for gas vehicles such as city buses and taxis, adapting to the transitional needs before the range upgrade of electric vehicles.

[0102] In summary, this invention, through the aforementioned embodiments, details a method for preparing a high-performance adsorbent for natural gas. This method system provides multiple optional or combined technical pathways, such as metal ion loading modification, mild thermal treatment modification, and surface chemical modification, which can flexibly and effectively solve the problems of single adsorbent performance and insufficient overall performance in existing technologies. Furthermore, the prepared adsorbents (especially those with precisely controlled pore size) can meet the needs of various scenarios, including LNG recovery, industrial operations, urban peak shaving, and remote energy supply. This provides a systematic and complete technical solution for preparing high-performance adsorbent products that combine high methane adsorption capacity, optimized pore structure, and excellent moisture resistance.

[0103] Verification Example 1: The ANG adsorbent obtained in Example 1 was used as the verification object.

[0104] The detection results of Example 1 are shown in Table 1.

[0105] Table 1

[0106]

[0107] Note: v / v = volume of adsorbed gas under standard conditions / volume of adsorbent.

[0108] The high-performance adsorbent prepared by the above method exhibits significantly improved performance. Testing revealed that its average pore size was precisely optimized from 3.1 nm to 3.4 nm, falling within the target range of 3.3–4 nm. At 25°C and 3.5 MPa, its volumetric adsorption capacity for methane increased dramatically from 125 v / v to 155 v / v, an increase of 24%, meeting the requirement of greater than or equal to 150 v / v for commercial applications. Correspondingly, its moisture resistance was also significantly improved. In a humid environment with a relative humidity of 80%, its water vapor adsorption rate decreased significantly from 8.2% to 5.5%, reducing competitive adsorption of water vapor and ensuring effective gas storage capacity under actual operating conditions. This embodiment successfully achieved simultaneous optimization of three key properties of the adsorbent through an integrated heat treatment step.

[0109] The key conclusion is:

[0110] 1. Although the metal loading slightly reduces the specific surface area, it significantly enhances the methane adsorption capacity (+24%) through Cu-CH4 interaction.

[0111] 2. After heat treatment, the average pore size is precisely expanded to 3.4nm, which is the optimal pore size for ANG, thereby improving the volumetric energy storage density.

[0112] 3. Enhanced surface hydrophobicity reduces water vapor interference.

[0113] Verification Example 2: The ANG adsorbent obtained in Example 2 was used as the verification object.

[0114] The adsorbent prepared in this embodiment exhibits further enhanced methane adsorption performance due to the loading of more reactive nickel species. Testing showed that, under the same conditions of 25°C and 3.5 MPa, its methane adsorption capacity reached 165 v / v, higher than that of the copper-modified adsorbent in Example 1. This indicates that the metal ion-loaded modification method proposed in this application has good versatility, allowing for further fine-tuning and optimization of adsorbent performance by selecting different metal ions. However, from a cost perspective, nickel salts are generally more expensive than copper salts; therefore, in practical applications, a suitable metal modifier can be selected based on performance requirements and cost budget.

[0115] Verification Example 3: The ANG adsorbent obtained in Example 3 was used as the verification object.

[0116] The adsorbent prepared in this embodiment exhibits significantly improved hydrophobic properties. Testing showed that, under 80% relative humidity, its water vapor adsorption rate was significantly reduced from 8.2% of the original activated carbon to below 4%, demonstrating extremely strong moisture resistance. When treating wet natural gas that has not been deeply dried, this type of adsorbent can minimize the competitive adsorption of water molecules, thereby ensuring the effective adsorption capacity of methane. Simultaneously, due to the potential pore structure annealing effect brought about by high-temperature treatment, its methane adsorption capacity is essentially the same as or slightly increased compared to the basic activated carbon. This embodiment demonstrates that the moisture resistance problem of adsorbents can be specifically addressed through specialized surface chemical modification.

[0117] Verification Example 4: The ANG adsorbent obtained in Example 4 was used as the verification object.

[0118] Testing revealed that, through the mild heat treatment method of this embodiment, the average pore size of the adsorbent was precisely controlled from 4.5 nm to 3.9 nm, successfully entering the target optimization range of 3.3–4 nm. The reduced pore size resulted in a higher size match between the adsorbent channels and methane molecules, enhancing the superposition effect of the adsorption potential within the pores, thereby effectively improving its methane storage capacity per unit volume under operating pressure. This embodiment demonstrates that mild heat treatment modification can effectively control the pore structure of activated carbon to meet the performance requirements of specific applications.

[0119] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. An application of an adsorbent, characterized in that, The adsorbent is used as an ANG adsorbent for adsorption-type natural gas, and the preparation method of the ANG adsorbent includes the following steps: (1) The wood raw material is crushed, screened, and impurities are removed to obtain pretreated raw material; wherein: The woody raw material is coconut shell; (2) The pretreated raw materials are sequentially subjected to carbonization, pyrolysis, and activation to generate a porous structure, thereby obtaining activated carbon; wherein: The carbonization and pyrolysis method is as follows: the pretreated raw materials are pyrolyzed under oxygen-deficient conditions at 400~900℃. (3) The activated carbon is cleaned and dried to prevent pore blockage, and dried activated carbon is obtained; (4) The dried activated carbon is pulverized and sieved to obtain pulverized activated carbon; (5) The pulverized activated carbon is post-treated and modified to adjust its surface chemical properties and pore size distribution, thereby enhancing its adsorption capacity for ANG, and finally obtaining the ANG adsorbent; wherein: The post-processing and modification method is a metal ion-supported modification method: The metal ion loading modification method includes the following steps: (SS1) Dissolve the modifier in water and add ethanol to obtain the impregnation solution; wherein: The modifier is NiCl2; The concentration of the modifier is 0.1~0.5 mol / L; (SS2) The pulverized activated carbon is added to the impregnation solution and stirred for adsorption; wherein: The stirring time is 2-4 hours, and the liquid-to-solid ratio is (1.5-2.5) mL:1g; (SS3) After filtration, discard the impregnation solution, retain the precipitate and dry it at 60~70℃ for 2~3 hours; (SS4) Under an inert atmosphere, the precipitate is heated to 380°C at a rate of 5~6°C / min and held at that temperature for 1~2 hours.

2. The application according to claim 1, characterized in that, In step (2), the activation method is as follows: the raw material after carbonization and pyrolysis is treated by physical activation, chemical activation, or a combination of physical and chemical activation; wherein: The physical activation method is as follows: the carbonized and pyrolyzed raw material is brought into contact with an activation gas at 800~1000℃, and the pores are enlarged by gas etching to form a microporous structure; the activation gas is water vapor or carbon dioxide. The chemical activation method is as follows: the raw material after carbonization and pyrolysis is mixed with a chemical activator to promote the formation of pores in the raw material; the chemical activator is phosphoric acid, zinc chloride, or potassium hydroxide. The physical-chemical combined activation method involves sequentially employing chemical activation and physical activation to optimize the pore structure and specific surface area of ​​the raw material.

3. The application according to claim 1, characterized in that, In step (3), the activated carbon is cleaned by acid washing or water washing.

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